(1) Field of the Invention
The present invention relates to the manufacture of fiber-reinforced polymer composite articles. Specifically, the invention relates to an apparatus and method for the manufacture of fiber-reinforced polymer composite articles wherein the resin is selectively distributed and controlled during the impregnation stage of the fiber reinforced articles.
(2) Description of Related Art
Fiber reinforced polymer composite articles have been available and in use for some time. Interest in these materials is due in part to their lightweight, high stiffness and strength, and corrosion-resistant properties. The transportation industry, for instance, has shown interest in the manufacture and use of fiber reinforced polymer composite materials due to the potential for increased fuel savings and the potential to carry increased payloads due to the reduced weight offered by the use of these types of materials. The lightweight, corrosion-resistant nature of these composite articles has also attracted the interest of the construction/infrastructure sectors.
Unfortunately, one of the key barriers to use of fiber-reinforced polymer composite articles has been the cost of their manufacture. The cost of the manufacture is significantly due to the labor required to produce such articles as well as the material waste incidental to such manufacture. Use of fiber-reinforced resin structures is difficult to justify when an acceptable, metal-based alternative may be available, often at a fraction of the cost.
Vacuum assisted resin transfer molding technology (VARTM) has been employed in manufacturing fiber-reinforced polymer composite structures. Described simply, processes employing VARTM generally use (1) a preform (i.e., a mold containing reinforcing fibers therein or thereon) to be impregnated with a resin; (2) a fluid impervious, flexible sheet, liner or bag (generally referred to as vacuum bag); (3) a vacuum; and (4) resin. In a VARTM type process, the preform is prepared in the desired shape, having the desired reinforcing fiber content and geometry then covered with a fluid impervious flexible sheet, liner or bag in such a manner such as to form a seal around or on the preform (vacuum bag). The vacuum bag has a resin port through which resin may be introduced. Liquid resin is then introduced into the vacuum bag at one end of the preform. A vacuum is then applied to the interior of the vacuum bag at the opposite end of the preform from where the resin is being introduced so as draw the resin across the preform and to collapse the vacuum bag against the preform. Once the preform is fully infused, the resin-containing preform is then cured and the vacuum bag removed. Use of a vacuum assists in the flow of the liquid resin within the preform. A description of vacuum assisted or vacuum bag techniques used to form fiber reinforced plastic structures is set forth in U.S. Pat. No. 4,902,215; and the description set forth therein is incorporated herein by reference.
U.S. Pat. No. 4,902,215 (Seemann III), issued Feb. 20, 1990, describes and claims a VARTM process known in the art as SCRIMP (Seemanns Composite Resin Infusion Molding Process). In addition to employing a VARTM process as generally described above, SCRIMP further employs a resin distribution medium positioned between the fabric lay up and the fluid impervious, flexible outer sheet (i.e., vacuum bag). This distribution medium serves to enhance the uniform distribution of resin across the top and through the fiber lay up upon the application of a vacuum by keeping the upper surface of the lay up and the lower surface of the fluid impervious outer sheet apart. In order to enhance the separation of the completed resin impregnated fiber lay up from the mold surface and the vacuum bag, porous peel plies which do not adhere to the resin are provided between the distribution media and the fiber lay up. After the resin has cured, the vacuum inlet is cut off, and the fluid impervious outer sheet, the distribution medium and peel ply are peeled from the fiber reinforced plastic structure.
U.S. Pat. No. 5,052,906 (Seemann), issued Oct. 1, 1991, describes and claims a modification/improvement to the claimed invention of Seemann, III ""215, described above. In order to facilitate resin flow, this patent describes the use of two resin distribution layers as opposed to one. One of said layers is placed/located on the mold surface per se, beneath the lower face of the fiber lay up, and the other on top of the fiber lay up, between the fiber lay up and the fluid impervious outer sheet. After the resin has been cured, the impervious outer sheet, the distribution mediums and peel plies are peeled from the resulting fiber reinforced structure (fiber reinforced lay up).
The VARTM processes described in these patents require the installation of distribution layer(s), peel ply, and, in some cases, a breather layer to ensure proper vacuum application during resin impregnation. These layers are used to provide a preferential flow path for the resin during the process and are disposable. Installation and removal of these materials can be time consuming and costly due to the specific labor involved. Furthermore, these layers become contaminated with resin as part of the impregnation process. Hence, these layers must be disposed of along with any residual resin that remains affixed to these consumable materials. It would be desirable to reduce the waste and labor associated with the manufacture of fiber reinforced resin structures using vacuum techniques.
U.S. Pat. No. 5,316,462 (Seemann), issued May 31, 1994, describes a VARTM process that does not employ a distribution medium of the type described above. Seemann ""462 describes and claims a unitary vacuum bag for use in forming fiber reinforced composite articles wherein the vacuum bag integrates the features of resin distribution and vacuum draw. For instance, U.S. Pat. No. ""462 describes that a multiplicity of cross channels may be formed on the inner surface of the vacuum bag to facilitate resin distribution. The vacuum bag taught may be cleaned and reused. The resulting fiber reinforced composite article would have embedded thereon an impression of these cross channels.
There remains a need to improve the VARTM type apparatus and processes. The present invention does not require the installation and removal of consumable resin distribution layers. Moreover, the present invention provides for superior resin flow paths using a novel means for establishing resin flow channels and provides for the resulting fiber reinforced composite article having a smooth surface thereon.
The present invention provides an apparatus and method for the manufacture of fiber-reinforced polymer composite articles using vacuum assisted resin transfer molding technology wherein some of the steps, labor and material waste associated with conventional, prior art VARTM manufacturing techniques are eliminated.
The process of the present invention has been termed FASTRAC, which refers to Fast Remotely Actuated Channeling. The FASTRAC process is a unique process that employs VARTM techniques in the general sense and operates without a traditional resin distribution medium. The FASTRAC process and apparatus employ a fluid impervious flexible outer sheet of the type referred to in the prior art in order to create a chamber around a fiber containing preform within which a vacuum can be applied via a primary vacuum line. This fluid impervious, flexible outer sheet is referred to herein as xe2x80x9cprimary vacuum bag.xe2x80x9dThe primary vacuum bag is used to seal a fiber containing preform to be impregnated with a resin to a mold (tool) surface. In the FASTRAC process and apparatus herein, the primary vacuum bag itself acts as the resin distribution medium via remote actuated channeling.
Once the primary vacuum bag has been installed, a resin channeling means (also referred to herein as FASTRAC layer) is placed on top of the primary vacuum bag that is in contact with the preform and a pocket created between and/or around the FASTRAC layer and the primary vacuum bag to which a second vacuum (also referred to herein as secondary vacuum) may be applied via a secondary vacuum line. The pocket is formed in a fashion so that upon activation of the secondary vacuum line, the primary vacuum bag is drawn up to the FASTRAC layer and caused to assume the channel configuration of the FASTRAC layer. How the pocket between the resin channeling means and the primary vacuum bag is formed may vary depending on the specific configuration of the resin channeling means employed.
The resin channeling means may be any means that when positioned on top of the primary vacuum bag and a secondary vacuum applied between and/or around said resin channeling means and the primary vacuum bag, the primary vacuum bag is caused to be drawn up into and/or around the resin channeling means and assume a channel configuration. The resin channeling means may, for example, be comprised of a rigid or semi rigid component part in the shape of a panel or strip having channels molded or machined thereon; it may be comprised of one or more rigid or semi rigid component parts in the shape of strips (with no channels molded thereon) positioned on top of the primary vacuum bag in a set configuration; or it may be one or more cords positioned on top of the primary vacuum bag to form a specific design. There is no limit as to what one may employ as the resin channeling means so long as the function described herein, that of forming channels in the primary vacuum bag (referred to herein as FASTRAC channels) as described, is achieved.
The pocket between and/or around the FASTRAC layer and the primary vacuum bag may be formed in a variety of manners. For instance, if the FASTRAC layer is a semi rigid solid strip or sheet having channels molded therein, the perimeter of this type of FASTRAC layer may be sealed to the primary vacuum bag, for instance, using conventional sealing means such as adhesives, duct tape, O-ring, etc. to form the pocket. If the FASTRAC layer, for example, comprises one or more cords positioned on the primary vacuum bag so as to generate a channel pattern on the primary vacuum bag, a second vacuum bag may be placed over the FASTRAC layer and the primary vacuum bag and sealed so as to provide a pocket within which a secondary vacuum may be applied. One having ordinary skill in the art would realize that use of a second vacuum bag as described may also be employed when the FASTRAC layer is a solid strip or sheet having channels molded therein. One having ordinary skill in the art, in view of the description of the invention herein, will be able to determine a variety of methods in which to form a pocket between a FASTRAC layer and the primary vacuum bag so that a secondary vacuum may be applied therein.
When a vacuum is drawn between the FASTRAC layer and the primary vacuum bag via a secondary vacuum line (also referred to herein as FASTRAC vacuum line), the primary vacuum bag is caused to be drawn up into or around the FASTRAC layer and assume the shape of channels. The channels formed in the primary vacuum bag are referred to herein as FASTRAC channels. As long as sufficient pressure drop is created between the FASTRAC layer and the primary vacuum bag via the secondary vacuum line, the temporary FASTRAC channels assumed by the primary vacuum bag remain in place.
In the practice of the present invention, once the FASTRAC layer has been set in place as described above, the primary vacuum line initiated, and the FASTRAC channels formed, resin is introduced into the primary vacuum bag via one or more resin input ports positioned beneath the FASTRAC layer so as to facilitate the flow of the resin along the fiber containing preform via the FASTRAC channels created. It is the FASTRAC channels created that assist in the distribution of the resin allowing the resin to flow across and then through the thickness of the preform once resin infusion is initiated.
During the exercise of the present invention, the vacuum differential between the primary and secondary vacuum lines can be adjusted so as to control the flow rate of the resin in the formed FASTRAC channels. For instance, slowly releasing the vacuum draw of the secondary vacuum line effects the shape and size of the FASTRAC channels assumed by the primary vacuum bag; and, hence effects the flow rate of the resin introduced into the preform. Once resin infusion of the preform is near complete, the secondary vacuum line is gradually released resulting in less defined FASTRAC channels which acts to slow the rate of resin flow to the preform. Upon complete resin impregnation of the preform, the secondary vacuum line is fully released causing the primary vacuum bag to no longer assume fretain any channel shape associated with the FASTRAC layer. The FASTRAC process thus uniquely eliminates these resin feed channels. Once the vacuum draw created by the secondary vacuum line has been completely eliminated, the primary vacuum bag is relaxed and collapses against the preform as a result of the vacuum draw present via operation of the primary vacuum line. Collapse of the primary vacuum bag forces the resin to remain within the shape of the fiber containing preform and helps create a smooth resin finish on the surface of the preform. The resin impregnated fiber containing preform may then be cured. Once cured, the primary vacuum bag is removed.
Throughout the above process, the primary vacuum line has been in operation facilitating the flow of the resin material through the fiber-containing preform. One having ordinary skill in the art would realize the most suitable location in which to position the primary vacuum line and the most suitable vacuum strength to employ so as to optimize resin impregnation of the preform.
Moreover, in exercising the present invention, one having ordinary skill in the art would recognize that the pressure differential beneath the primary vacuum bag and above the primary vacuum bag determines the formation, or lack thereof, of FASTRAC channels in the primary vacuum bag. One having ordinary skill in the art would recognize that it is essential that the pressure differential beneath the primary vacuum bag and above the primary vacuum bag must always be such as to permit the primary vacuum bag to conform to the shape of the FASTRAC channels in order to optimize/maximize resin flow to the preform. Vacuum levels are ideally 30xe2x80x3 Hg, but, more realistically, commercially available vacuum pumps supply a vacuum level of between 28-29xe2x80x3 Hg. Other vacuum levels may be employed herein. One having ordinary skill in the art will recognize that in the exercise of the present invention it is not the vacuum levels per se that are critical, but the pressure differential between the pressure beneath the primary vacuum bag and above the primary vacuum bag that is critical in operation of the invention. This may be adjusted so as to accommodate the specific needs of one practicing the invention.
It is an object of the present invention to provide a resin distribution system having superior performance as compared to conventional VARTM technology.
It is an object of the present invention to provide a novel and flexible means for establishing resin flow channels in a VARTM type process.
An object of the present invention is to provide an apparatus and method for the manufacture of fiber-reinforced polymer composite articles employing resin channeling means that do not come into direct contact with the resin.
It is an object of the present invention to provide an apparatus and method for the manufacture of fiber-reinforced polymer composite articles using vacuum assisted resin transfer wherein excess waste is reduced and/or eliminated.
A further object of the invention is to provide an apparatus and method for the manufacture of fiber-reinforced polymer composite articles using vacuum assisted resin transfer technology wherein labor associated with the fabrication of said articles is reduced.
A further object of the invention is to provide a vacuum assisted resin distribution system having a means for actively steering the resin flow front to minimize or eliminate resin waste and to minimize total resin fill time of fiber reinforced articles.
Still a further object of the present invention is to provide a means for separately establishing and controlling both the resin impregnation pressure differential and local flow channel permeability.
Yet a further object of the invention is to provide modular means for rapidly configuring resin flow paths.
The means to achieve these and other objectives of the present invention will be apparent from the following detailed description of the invention, drawings and claims.